/*
 ** $Id: lgc.c,v 2.38.1.1 2007/12/27 13:02:25 roberto Exp $
 ** Garbage Collector
 ** See Copyright Notice in lua.h
 */

#include <string.h>

#define lgc_c
#define LUA_CORE

#include "lua.h"

#include "ldebug.h"
#include "ldo.h"
#include "lfunc.h"
#include "lgc.h"
#include "lmem.h"
#include "lobject.h"
#include "lstate.h"
#include "lstring.h"
#include "ltable.h"
#include "ltm.h"


#define GCSTEPSIZE	1024u
#define GCSWEEPMAX	40
#define GCSWEEPCOST	10
#define GCFINALIZECOST	100


#define maskmarks	cast_byte(~(bitmask(BLACKBIT)|WHITEBITS))

#define makewhite(g,x)	\
((x)->gch.marked = cast_byte(((x)->gch.marked & maskmarks) | luaC_white(g)))

#define white2gray(x)	reset2bits((x)->gch.marked, WHITE0BIT, WHITE1BIT)
#define black2gray(x)	resetbit((x)->gch.marked, BLACKBIT)

#define stringmark(s)	reset2bits((s)->tsv.marked, WHITE0BIT, WHITE1BIT)


#define isfinalized(u)		testbit((u)->marked, FINALIZEDBIT)
#define markfinalized(u)	l_setbit((u)->marked, FINALIZEDBIT)


#define KEYWEAK         bitmask(KEYWEAKBIT)
#define VALUEWEAK       bitmask(VALUEWEAKBIT)



#define markvalue(g,o) { checkconsistency(o); \
if (iscollectable(o) && iswhite(gcvalue(o))) reallymarkobject(g,gcvalue(o)); }

#define markobject(g,t) { if (iswhite(obj2gco(t))) \
reallymarkobject(g, obj2gco(t)); }


#define setthreshold(g)  (g->GCthreshold = (g->estimate/100) * g->gcpause)


static void removeentry (Node *n) {
    lua_assert(ttisnil(gval(n)));
    if (iscollectable(gkey(n)))
        setttype(gkey(n), LUA_TDEADKEY);  /* dead key; remove it */
}


static void reallymarkobject (global_State *g, GCObject *o) {
    lua_assert(iswhite(o) && !isdead(g, o));
    white2gray(o);
    switch (o->gch.tt) {
        case LUA_TSTRING: {
            return;
        }
        case LUA_TUSERDATA: {
            Table *mt = gco2u(o)->metatable;
            gray2black(o);  /* udata are never gray */
            if (mt) markobject(g, mt);
            markobject(g, gco2u(o)->env);
            return;
        }
        case LUA_TUPVAL: {
            UpVal *uv = gco2uv(o);
            markvalue(g, uv->v);
            if (uv->v == &uv->u.value)  /* closed? */
                gray2black(o);  /* open upvalues are never black */
            return;
        }
        case LUA_TFUNCTION: {
            gco2cl(o)->c.gclist = g->gray;
            g->gray = o;
            break;
        }
        case LUA_TTABLE: {
            gco2h(o)->gclist = g->gray;
            g->gray = o;
            break;
        }
        case LUA_TTHREAD: {
            gco2th(o)->gclist = g->gray;
            g->gray = o;
            break;
        }
        case LUA_TPROTO: {
            gco2p(o)->gclist = g->gray;
            g->gray = o;
            break;
        }
        default: lua_assert(0);
    }
}


static void marktmu (global_State *g) {
    GCObject *u = g->tmudata;
    if (u) {
        do {
            u = u->gch.next;
            makewhite(g, u);  /* may be marked, if left from previous GC */
            reallymarkobject(g, u);
        } while (u != g->tmudata);
    }
}


/* move `dead' udata that need finalization to list `tmudata' */
size_t luaC_separateudata (lua_State *L, int all) {
    global_State *g = G(L);
    size_t deadmem = 0;
    GCObject **p = &g->mainthread->next;
    GCObject *curr;
    while ((curr = *p) != NULL) {
        if (!(iswhite(curr) || all) || isfinalized(gco2u(curr)))
            p = &curr->gch.next;  /* don't bother with them */
        else if (fasttm(L, gco2u(curr)->metatable, TM_GC) == NULL) {
            markfinalized(gco2u(curr));  /* don't need finalization */
            p = &curr->gch.next;
        }
        else {  /* must call its gc method */
            deadmem += sizeudata(gco2u(curr));
            markfinalized(gco2u(curr));
            *p = curr->gch.next;
            /* link `curr' at the end of `tmudata' list */
            if (g->tmudata == NULL)  /* list is empty? */
                g->tmudata = curr->gch.next = curr;  /* creates a circular list */
            else {
                curr->gch.next = g->tmudata->gch.next;
                g->tmudata->gch.next = curr;
                g->tmudata = curr;
            }
        }
    }
    return deadmem;
}


static int traversetable (global_State *g, Table *h) {
    int i;
    int weakkey = 0;
    int weakvalue = 0;
    const TValue *mode;
    if (h->metatable)
        markobject(g, h->metatable);
    mode = gfasttm(g, h->metatable, TM_MODE);
    if (mode && ttisstring(mode)) {  /* is there a weak mode? */
        weakkey = (strchr(svalue(mode), 'k') != NULL);
        weakvalue = (strchr(svalue(mode), 'v') != NULL);
        if (weakkey || weakvalue) {  /* is really weak? */
            h->marked &= ~(KEYWEAK | VALUEWEAK);  /* clear bits */
            h->marked |= cast_byte((weakkey << KEYWEAKBIT) |
                                   (weakvalue << VALUEWEAKBIT));
            h->gclist = g->weak;  /* must be cleared after GC, ... */
            g->weak = obj2gco(h);  /* ... so put in the appropriate list */
        }
    }
    if (weakkey && weakvalue) return 1;
    if (!weakvalue) {
        i = h->sizearray;
        while (i--)
            markvalue(g, &h->array[i]);
    }
    i = sizenode(h);
    while (i--) {
        Node *n = gnode(h, i);
        lua_assert(ttype(gkey(n)) != LUA_TDEADKEY || ttisnil(gval(n)));
        if (ttisnil(gval(n)))
            removeentry(n);  /* remove empty entries */
        else {
            lua_assert(!ttisnil(gkey(n)));
            if (!weakkey) markvalue(g, gkey(n));
            if (!weakvalue) markvalue(g, gval(n));
        }
    }
    return weakkey || weakvalue;
}


/*
 ** All marks are conditional because a GC may happen while the
 ** prototype is still being created
 */
static void traverseproto (global_State *g, Proto *f) {
    int i;
    if (f->source) stringmark(f->source);
    for (i=0; i<f->sizek; i++)  /* mark literals */
        markvalue(g, &f->k[i]);
    for (i=0; i<f->sizeupvalues; i++) {  /* mark upvalue names */
        if (f->upvalues[i])
            stringmark(f->upvalues[i]);
    }
    for (i=0; i<f->sizep; i++) {  /* mark nested protos */
        if (f->p[i])
            markobject(g, f->p[i]);
    }
    for (i=0; i<f->sizelocvars; i++) {  /* mark local-variable names */
        if (f->locvars[i].varname)
            stringmark(f->locvars[i].varname);
    }
}



static void traverseclosure (global_State *g, Closure *cl) {
    markobject(g, cl->c.env);
    if (cl->c.isC) {
        int i;
        for (i=0; i<cl->c.nupvalues; i++)  /* mark its upvalues */
            markvalue(g, &cl->c.upvalue[i]);
    }
    else {
        int i;
        lua_assert(cl->l.nupvalues == cl->l.p->nups);
        markobject(g, cl->l.p);
        for (i=0; i<cl->l.nupvalues; i++)  /* mark its upvalues */
            markobject(g, cl->l.upvals[i]);
    }
}


static void checkstacksizes (lua_State *L, StkId max) {
    int ci_used = cast_int(L->ci - L->base_ci);  /* number of `ci' in use */
    int s_used = cast_int(max - L->stack);  /* part of stack in use */
    if (L->size_ci > LUAI_MAXCALLS)  /* handling overflow? */
        return;  /* do not touch the stacks */
    if (4*ci_used < L->size_ci && 2*BASIC_CI_SIZE < L->size_ci)
        luaD_reallocCI(L, L->size_ci/2);  /* still big enough... */
    condhardstacktests(luaD_reallocCI(L, ci_used + 1));
    if (4*s_used < L->stacksize &&
        2*(BASIC_STACK_SIZE+EXTRA_STACK) < L->stacksize)
        luaD_reallocstack(L, L->stacksize/2);  /* still big enough... */
    condhardstacktests(luaD_reallocstack(L, s_used));
}


static void traversestack (global_State *g, lua_State *l) {
    StkId o, lim;
    CallInfo *ci;
    markvalue(g, gt(l));
    lim = l->top;
    for (ci = l->base_ci; ci <= l->ci; ci++) {
        lua_assert(ci->top <= l->stack_last);
        if (lim < ci->top) lim = ci->top;
    }
    for (o = l->stack; o < l->top; o++)
        markvalue(g, o);
    for (; o <= lim; o++)
        setnilvalue(o);
    checkstacksizes(l, lim);
}


/*
 ** traverse one gray object, turning it to black.
 ** Returns `quantity' traversed.
 */
static l_mem propagatemark (global_State *g) {
    GCObject *o = g->gray;
    lua_assert(isgray(o));
    gray2black(o);
    switch (o->gch.tt) {
        case LUA_TTABLE: {
            Table *h = gco2h(o);
            g->gray = h->gclist;
            if (traversetable(g, h))  /* table is weak? */
                black2gray(o);  /* keep it gray */
            return sizeof(Table) + sizeof(TValue) * h->sizearray +
            sizeof(Node) * sizenode(h);
        }
        case LUA_TFUNCTION: {
            Closure *cl = gco2cl(o);
            g->gray = cl->c.gclist;
            traverseclosure(g, cl);
            return (cl->c.isC) ? sizeCclosure(cl->c.nupvalues) :
            sizeLclosure(cl->l.nupvalues);
        }
        case LUA_TTHREAD: {
            lua_State *th = gco2th(o);
            g->gray = th->gclist;
            th->gclist = g->grayagain;
            g->grayagain = o;
            black2gray(o);
            traversestack(g, th);
            return sizeof(lua_State) + sizeof(TValue) * th->stacksize +
            sizeof(CallInfo) * th->size_ci;
        }
        case LUA_TPROTO: {
            Proto *p = gco2p(o);
            g->gray = p->gclist;
            traverseproto(g, p);
            return sizeof(Proto) + sizeof(Instruction) * p->sizecode +
            sizeof(Proto *) * p->sizep +
            sizeof(TValue) * p->sizek + 
            sizeof(int) * p->sizelineinfo +
            sizeof(LocVar) * p->sizelocvars +
            sizeof(TString *) * p->sizeupvalues;
        }
        default: lua_assert(0); return 0;
    }
}


static size_t propagateall (global_State *g) {
    size_t m = 0;
    while (g->gray) m += propagatemark(g);
    return m;
}


/*
 ** The next function tells whether a key or value can be cleared from
 ** a weak table. Non-collectable objects are never removed from weak
 ** tables. Strings behave as `values', so are never removed too. for
 ** other objects: if really collected, cannot keep them; for userdata
 ** being finalized, keep them in keys, but not in values
 */
static int iscleared (const TValue *o, int iskey) {
    if (!iscollectable(o)) return 0;
    if (ttisstring(o)) {
        stringmark(rawtsvalue(o));  /* strings are `values', so are never weak */
        return 0;
    }
    return iswhite(gcvalue(o)) ||
    (ttisuserdata(o) && (!iskey && isfinalized(uvalue(o))));
}


/*
 ** clear collected entries from weaktables
 */
static void cleartable (GCObject *l) {
    while (l) {
        Table *h = gco2h(l);
        int i = h->sizearray;
        lua_assert(testbit(h->marked, VALUEWEAKBIT) ||
                   testbit(h->marked, KEYWEAKBIT));
        if (testbit(h->marked, VALUEWEAKBIT)) {
            while (i--) {
                TValue *o = &h->array[i];
                if (iscleared(o, 0))  /* value was collected? */
                    setnilvalue(o);  /* remove value */
            }
        }
        i = sizenode(h);
        while (i--) {
            Node *n = gnode(h, i);
            if (!ttisnil(gval(n)) &&  /* non-empty entry? */
                (iscleared(key2tval(n), 1) || iscleared(gval(n), 0))) {
                setnilvalue(gval(n));  /* remove value ... */
                removeentry(n);  /* remove entry from table */
            }
        }
        l = h->gclist;
    }
}


static void freeobj (lua_State *L, GCObject *o) {
    switch (o->gch.tt) {
        case LUA_TPROTO: luaF_freeproto(L, gco2p(o)); break;
        case LUA_TFUNCTION: luaF_freeclosure(L, gco2cl(o)); break;
        case LUA_TUPVAL: luaF_freeupval(L, gco2uv(o)); break;
        case LUA_TTABLE: luaH_free(L, gco2h(o)); break;
        case LUA_TTHREAD: {
            lua_assert(gco2th(o) != L && gco2th(o) != G(L)->mainthread);
            luaE_freethread(L, gco2th(o));
            break;
        }
        case LUA_TSTRING: {
            G(L)->strt.nuse--;
            luaM_freemem(L, o, sizestring(gco2ts(o)));
            break;
        }
        case LUA_TUSERDATA: {
            luaM_freemem(L, o, sizeudata(gco2u(o)));
            break;
        }
        default: lua_assert(0);
    }
}



#define sweepwholelist(L,p)	sweeplist(L,p,MAX_LUMEM)


static GCObject **sweeplist (lua_State *L, GCObject **p, lu_mem count) {
    GCObject *curr;
    global_State *g = G(L);
    int deadmask = otherwhite(g);
    while ((curr = *p) != NULL && count-- > 0) {
        if (curr->gch.tt == LUA_TTHREAD)  /* sweep open upvalues of each thread */
            sweepwholelist(L, &gco2th(curr)->openupval);
        if ((curr->gch.marked ^ WHITEBITS) & deadmask) {  /* not dead? */
            lua_assert(!isdead(g, curr) || testbit(curr->gch.marked, FIXEDBIT));
            makewhite(g, curr);  /* make it white (for next cycle) */
            p = &curr->gch.next;
        }
        else {  /* must erase `curr' */
            lua_assert(isdead(g, curr) || deadmask == bitmask(SFIXEDBIT));
            *p = curr->gch.next;
            if (curr == g->rootgc)  /* is the first element of the list? */
                g->rootgc = curr->gch.next;  /* adjust first */
            freeobj(L, curr);
        }
    }
    return p;
}


static void checkSizes (lua_State *L) {
    global_State *g = G(L);
    /* check size of string hash */
    if (g->strt.nuse < cast(lu_int32, g->strt.size/4) &&
        g->strt.size > MINSTRTABSIZE*2)
        luaS_resize(L, g->strt.size/2);  /* table is too big */
    /* check size of buffer */
    if (luaZ_sizebuffer(&g->buff) > LUA_MINBUFFER*2) {  /* buffer too big? */
        size_t newsize = luaZ_sizebuffer(&g->buff) / 2;
        luaZ_resizebuffer(L, &g->buff, newsize);
    }
}


static void GCTM (lua_State *L) {
    global_State *g = G(L);
    GCObject *o = g->tmudata->gch.next;  /* get first element */
    Udata *udata = rawgco2u(o);
    const TValue *tm;
    /* remove udata from `tmudata' */
    if (o == g->tmudata)  /* last element? */
        g->tmudata = NULL;
    else
        g->tmudata->gch.next = udata->uv.next;
    udata->uv.next = g->mainthread->next;  /* return it to `root' list */
    g->mainthread->next = o;
    makewhite(g, o);
    tm = fasttm(L, udata->uv.metatable, TM_GC);
    if (tm != NULL) {
        lu_byte oldah = L->allowhook;
        lu_mem oldt = g->GCthreshold;
        L->allowhook = 0;  /* stop debug hooks during GC tag method */
        g->GCthreshold = 2*g->totalbytes;  /* avoid GC steps */
        setobj2s(L, L->top, tm);
        setuvalue(L, L->top+1, udata);
        L->top += 2;
        luaD_call(L, L->top - 2, 0);
        L->allowhook = oldah;  /* restore hooks */
        g->GCthreshold = oldt;  /* restore threshold */
    }
}


/*
 ** Call all GC tag methods
 */
void luaC_callGCTM (lua_State *L) {
    while (G(L)->tmudata)
        GCTM(L);
}


void luaC_freeall (lua_State *L) {
    global_State *g = G(L);
    int i;
    g->currentwhite = WHITEBITS | bitmask(SFIXEDBIT);  /* mask to collect all elements */
    sweepwholelist(L, &g->rootgc);
    for (i = 0; i < g->strt.size; i++)  /* free all string lists */
        sweepwholelist(L, &g->strt.hash[i]);
}


static void markmt (global_State *g) {
    int i;
    for (i=0; i<NUM_TAGS; i++)
        if (g->mt[i]) markobject(g, g->mt[i]);
}


/* mark root set */
static void markroot (lua_State *L) {
    global_State *g = G(L);
    g->gray = NULL;
    g->grayagain = NULL;
    g->weak = NULL;
    markobject(g, g->mainthread);
    /* make global table be traversed before main stack */
    markvalue(g, gt(g->mainthread));
    markvalue(g, registry(L));
    markmt(g);
    g->gcstate = GCSpropagate;
}


static void remarkupvals (global_State *g) {
    UpVal *uv;
    for (uv = g->uvhead.u.l.next; uv != &g->uvhead; uv = uv->u.l.next) {
        lua_assert(uv->u.l.next->u.l.prev == uv && uv->u.l.prev->u.l.next == uv);
        if (isgray(obj2gco(uv)))
            markvalue(g, uv->v);
    }
}


static void atomic (lua_State *L) {
    global_State *g = G(L);
    size_t udsize;  /* total size of userdata to be finalized */
    /* remark occasional upvalues of (maybe) dead threads */
    remarkupvals(g);
    /* traverse objects cautch by write barrier and by 'remarkupvals' */
    propagateall(g);
    /* remark weak tables */
    g->gray = g->weak;
    g->weak = NULL;
    lua_assert(!iswhite(obj2gco(g->mainthread)));
    markobject(g, L);  /* mark running thread */
    markmt(g);  /* mark basic metatables (again) */
    propagateall(g);
    /* remark gray again */
    g->gray = g->grayagain;
    g->grayagain = NULL;
    propagateall(g);
    udsize = luaC_separateudata(L, 0);  /* separate userdata to be finalized */
    marktmu(g);  /* mark `preserved' userdata */
    udsize += propagateall(g);  /* remark, to propagate `preserveness' */
    cleartable(g->weak);  /* remove collected objects from weak tables */
    /* flip current white */
    g->currentwhite = cast_byte(otherwhite(g));
    g->sweepstrgc = 0;
    g->sweepgc = &g->rootgc;
    g->gcstate = GCSsweepstring;
    g->estimate = g->totalbytes - udsize;  /* first estimate */
}


static l_mem singlestep (lua_State *L) {
    global_State *g = G(L);
    /*lua_checkmemory(L);*/
    switch (g->gcstate) {
        case GCSpause: {
            markroot(L);  /* start a new collection */
            return 0;
        }
        case GCSpropagate: {
            if (g->gray)
                return propagatemark(g);
            else {  /* no more `gray' objects */
                atomic(L);  /* finish mark phase */
                return 0;
            }
        }
        case GCSsweepstring: {
            lu_mem old = g->totalbytes;
            sweepwholelist(L, &g->strt.hash[g->sweepstrgc++]);
            if (g->sweepstrgc >= g->strt.size)  /* nothing more to sweep? */
                g->gcstate = GCSsweep;  /* end sweep-string phase */
            lua_assert(old >= g->totalbytes);
            g->estimate -= old - g->totalbytes;
            return GCSWEEPCOST;
        }
        case GCSsweep: {
            lu_mem old = g->totalbytes;
            g->sweepgc = sweeplist(L, g->sweepgc, GCSWEEPMAX);
            if (*g->sweepgc == NULL) {  /* nothing more to sweep? */
                checkSizes(L);
                g->gcstate = GCSfinalize;  /* end sweep phase */
            }
            lua_assert(old >= g->totalbytes);
            g->estimate -= old - g->totalbytes;
            return GCSWEEPMAX*GCSWEEPCOST;
        }
        case GCSfinalize: {
            if (g->tmudata) {
                GCTM(L);
                if (g->estimate > GCFINALIZECOST)
                    g->estimate -= GCFINALIZECOST;
                return GCFINALIZECOST;
            }
            else {
                g->gcstate = GCSpause;  /* end collection */
                g->gcdept = 0;
                return 0;
            }
        }
        default: lua_assert(0); return 0;
    }
}


void luaC_step (lua_State *L) {
    global_State *g = G(L);
    l_mem lim = (GCSTEPSIZE/100) * g->gcstepmul;
    if (lim == 0)
        lim = (MAX_LUMEM-1)/2;  /* no limit */
    g->gcdept += g->totalbytes - g->GCthreshold;
    do {
        lim -= singlestep(L);
        if (g->gcstate == GCSpause)
            break;
    } while (lim > 0);
    if (g->gcstate != GCSpause) {
        if (g->gcdept < GCSTEPSIZE)
            g->GCthreshold = g->totalbytes + GCSTEPSIZE;  /* - lim/g->gcstepmul;*/
        else {
            g->gcdept -= GCSTEPSIZE;
            g->GCthreshold = g->totalbytes;
        }
    }
    else {
        lua_assert(g->totalbytes >= g->estimate);
        setthreshold(g);
    }
}


void luaC_fullgc (lua_State *L) {
    global_State *g = G(L);
    if (g->gcstate <= GCSpropagate) {
        /* reset sweep marks to sweep all elements (returning them to white) */
        g->sweepstrgc = 0;
        g->sweepgc = &g->rootgc;
        /* reset other collector lists */
        g->gray = NULL;
        g->grayagain = NULL;
        g->weak = NULL;
        g->gcstate = GCSsweepstring;
    }
    lua_assert(g->gcstate != GCSpause && g->gcstate != GCSpropagate);
    /* finish any pending sweep phase */
    while (g->gcstate != GCSfinalize) {
        lua_assert(g->gcstate == GCSsweepstring || g->gcstate == GCSsweep);
        singlestep(L);
    }
    markroot(L);
    while (g->gcstate != GCSpause) {
        singlestep(L);
    }
    setthreshold(g);
}


void luaC_barrierf (lua_State *L, GCObject *o, GCObject *v) {
    global_State *g = G(L);
    lua_assert(isblack(o) && iswhite(v) && !isdead(g, v) && !isdead(g, o));
    lua_assert(g->gcstate != GCSfinalize && g->gcstate != GCSpause);
    lua_assert(ttype(&o->gch) != LUA_TTABLE);
    /* must keep invariant? */
    if (g->gcstate == GCSpropagate)
        reallymarkobject(g, v);  /* restore invariant */
    else  /* don't mind */
        makewhite(g, o);  /* mark as white just to avoid other barriers */
}


void luaC_barrierback (lua_State *L, Table *t) {
    global_State *g = G(L);
    GCObject *o = obj2gco(t);
    lua_assert(isblack(o) && !isdead(g, o));
    lua_assert(g->gcstate != GCSfinalize && g->gcstate != GCSpause);
    black2gray(o);  /* make table gray (again) */
    t->gclist = g->grayagain;
    g->grayagain = o;
}


void luaC_link (lua_State *L, GCObject *o, lu_byte tt) {
    global_State *g = G(L);
    o->gch.next = g->rootgc;
    g->rootgc = o;
    o->gch.marked = luaC_white(g);
    o->gch.tt = tt;
}


void luaC_linkupval (lua_State *L, UpVal *uv) {
    global_State *g = G(L);
    GCObject *o = obj2gco(uv);
    o->gch.next = g->rootgc;  /* link upvalue into `rootgc' list */
    g->rootgc = o;
    if (isgray(o)) { 
        if (g->gcstate == GCSpropagate) {
            gray2black(o);  /* closed upvalues need barrier */
            luaC_barrier(L, uv, uv->v);
        }
        else {  /* sweep phase: sweep it (turning it into white) */
            makewhite(g, o);
            lua_assert(g->gcstate != GCSfinalize && g->gcstate != GCSpause);
        }
    }
}

